Dialysis machine support assemblies and related systems and methods

ABSTRACT

In some aspects, a dialysis machine support assembly includes a platform configured to support a dialysis machine and a drive assembly configured to move the platform vertically.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority under 35U.S.C. § 120 to U.S. application Ser. No. 13/286,586, filed on Nov. 1,2011. The contents of this priority application are hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

This invention relates to dialysis machine support assemblies andrelated systems and methods.

BACKGROUND

Dialysis is a treatment used to support a patient with insufficientrenal function. The two principal dialysis methods are hemodialysis andperitoneal dialysis.

During hemodialysis (“HD”), the patient's blood is passed through adialyzer of a dialysis machine while also passing a dialysis solution ordialysate through the dialyzer. A semi-permeable membrane in thedialyzer separates the blood from the dialysate within the dialyzer andallows diffusion and osmosis exchanges to take place between thedialysate and the blood stream. These exchanges across the membraneresult in the removal of waste products, including solutes like urea andcreatinine, from the blood. These exchanges also regulate the levels ofother substances, such as sodium and water, in the blood. In this way,the dialysis machine acts as an artificial kidney for cleansing theblood.

During peritoneal dialysis (“PD”), a patient's peritoneal cavity isperiodically infused with dialysis solution or dialysate. The membranouslining of the patient's peritoneum acts as a natural semi-permeablemembrane that allows diffusion and osmosis exchanges to take placebetween the solution and the blood stream. These exchanges across thepatient's peritoneum, like the continuous exchange across the dialyzerin HD, result in the removal of waste products, including solutes likeurea and creatinine, from the blood, and regulate the levels of othersubstances, such as sodium and water, in the blood.

Many PD cyclers are designed to automatically infuse, dwell, and draindialysate to and from the patient's peritoneal cavity. The treatmenttypically lasts for several hours, often beginning with an initial drainprocedure to empty the peritoneal cavity of used or spent dialysate. Thesequence then proceeds through the succession of fill, dwell, and drainphases that follow one after the other. Each phase is called a cycle.

SUMMARY

In one aspect of the invention, a dialysis machine support assemblyincludes a platform configured to support a dialysis machine, and adrive assembly configured to move the platform vertically.

Implementations can include one or more of the following features.

In some implementations, the drive assembly is configured to becontrolled by the dialysis machine.

In some implementations, the drive assembly can move the platform alonga vertical distance that is 24-48 inches.

In some implementations, the dialysis machine support assembly includesa control unit that is electrically connected to the drive assembly andis configured to operate the drive assembly to move and position theplatform vertically.

In some implementations, the dialysis machine support assembly includesa device configured to prevent the platform from rotating about thedrive assembly when the platform moves vertically.

In some implementations, the drive assembly includes a leadscrew fixedto a base, a leadscrew nut that is rotatably coupled to the platform andconfigured to engage the leadscrew, and a motor that is mechanicallyconnected to the leadscrew nut and configured to rotate the leadscrewnut.

In some implementations, the motor is an electric motor configured to beelectrically connected to the dialysis machine or to an external controlunit.

In some implementations, the leadscrew has a recess formedlongitudinally along the leadscrew, and the platform has a tab that issized to fit within the recess and travel along the recess when theplatform moves vertically.

In some implementations, the dialysis machine support assembly includesmultiple legs and a stationary platform disposed on top of the multiplelegs.

In some implementations, the dialysis machine support assembly includesa base from which the multiple legs extend upwardly.

In some implementations, the dialysis machine support assembly includesmultiple wheels secured to the bottom of the base to support thedialysis machine support assembly.

In another aspect of the invention, a dialysis system includes adialysis machine; and a dialysis machine support assembly that includesa platform configured to support the dialysis machine, and a driveassembly configured to move the platform vertically, where the dialysismachine is disposed on the platform.

Implementations can include one or more of the following features.

In some implementations, the dialysis machine is electrically connectedto the drive assembly and configured to operate the drive assembly tomove and position the platform vertically.

In some implementations, the dialysis machine includes pressure sensorsto measure pressure in a fluid path between fluid pump chambers of thedialysis machine and a patient.

In some implementations, the dialysis machine is a peritoneal dialysiscycler.

In another aspect of the invention, a dialysis machine support assemblyincludes a base, multiple wheels disposed along a bottom surface of thebase, a drive assembly extending upward from the base that is configuredto be electrically connected to a dialysis machine, a verticallymoveable platform secured to a moving portion of the drive assembly, thevertically moveable platform being configured to support the dialysismachine, and the position of the vertically moveable platform beingcontrolled by the drive assembly, multiple legs extending upward fromthe base, a stationary platform disposed on top of the multiple legs,the stationary platform defining a recess that is sized to receive thevertically moveable platform, and multiple hooks extending from thesides of the stationary platform, the hooks being configured to supportdialysate bags fluidly connected to the dialysis machine during adialysis treatment, where the drive assembly is configured to move thevertically moveable platform above and below a height at which a patientis positioned during a dialysis treatment.

In a further aspect of the invention, a method includes monitoringpressure in a fluid path between a dialysis fluid pump chamber and apatient, and adjusting a vertical position of a dialysis machine whenmonitored pressure exceeds a maximum pressure or falls below a minimumpressure.

Implementations can include one or more of the following features.

In some implementations, the method further includes adjusting a rate atwhich fluid is pump to or from a patient along the fluid path.

In some implementations, adjusting a vertical position when monitoredpressure exceeds a maximum pressure includes moving the dialysis machineupward vertically while fluid is being provided to a patient.

In some implementations, the maximum pressure is 150-200 mbar.

In some implementations, the method further includes reducing a rate atwhich fluid is pumped to the patient.

In some implementations, adjusting a vertical position when monitoredpressure falls below a minimum pressure includes moving the dialysismachine downward vertically while fluid is being removed from a patient.

In some implementations, the minimum pressure is (−150)-(−200) mbar.

In some implementations, the method further includes reducing a rate atwhich fluid is pumped from the patient.

Implementations can include one or more of the following advantages.

Systems and methods described herein can be used to optimize filling anddraining cycles of dialysis treatments by raising and/or lowering adialysis cycler relative to a patient in order to maximize flow rates ofdialysis solution.

Additionally, methods described herein can be used to avoid signalingalarms and/or disturbing a patient during dialysis treatments byautomatically responding to elevated, potentially dangerous levels offluid resistance measured within a patient line during filling anddraining cycles of dialysis treatments by raising and/or lowering adialysis cycler relative to a patient.

DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a peritoneal dialysis (PD) cycler on acart that has a vertically moveable platform.

FIG. 2 is a perspective view of the cart of FIG. 1.

FIG. 3 is a perspective view of the PD cycler of FIG. 1 along with a PDcassette to be used with the PD cycler. A door of the PD cycler is inthe open position to show the inner surfaces of the PD cycler thatinterface with the PD cassette during use.

FIG. 4 is a perspective view of an open cassette compartment of the PDcycler of FIG. 1, showing, among other things, pistons having pistonheads that include mechanisms that can be used to mechanically connectthe piston heads to associated dome-shaped members of the PD cassette.

FIG. 5 is a perspective, cross-sectional view of the PD cassette of FIG.3.

FIG. 6 is a perspective view of the PD cassette of FIG. 3, from aflexible membrane and dome-shaped fastening member side of the PDcassette.

FIG. 7 is a perspective view of the PD cassette of FIG. 3, from a rigidbase side of the PD cassette.

FIG. 8 is a partial perspective view of the PD cassette in the cassettecompartment of the PD cycler FIG. 3.

DETAILED DESCRIPTION

This disclosure relates generally to dialysis machine support assembliesand related systems and methods. In some cases, a dialysis machinesupport assembly (e.g., a cart) includes a vertically movable platformconfigured to support a dialysis machine (e.g., a PD cycler). Duringdialysis treatments, the dialysis machine can be seated on the platformthat moves vertically relative to a patient. The height of the platformand the dialysis machine can be controlled based on the pressure orresistance measured within a fluid line or compartment located along afluid flow path between the dialysis machine and the patient. Forexample, the height of the platform and the dialysis machine can becontrolled in a manner to maintain a desired flow rate of fluid passingfrom the dialysis machine to the patient or vice versa. The dialysismachine support assembly can be used to safely and effectivelyaccommodate for spikes in fluid resistance pressure within linesconnected to the patient, which could otherwise cause an alarm thatwould disturb the patient and require attention. The systems and methodsdescribed herein of using the cart during dialysis treatments to raiseand lower the dialysis machine can be used to optimize the flow of fluidto and/or from the patient.

FIG. 1 shows a PD cycler 100 seated on a cart 50. As discussed herein,the PD cycler 100 is used to deliver PD solution (e.g., dialysate) toand drain fluid from a patient during PD treatments.

Cart

As shown in FIG. 2, the cart 50 includes a base 52, multiple (e.g.,three) wheels 54, a vertically moveable platform 56, a table platform58, and a drive assembly 60 to move the vertically moveable platform 56upward and downward.

The base 52 is a substantially flat, planar member that is mounted ontop of the wheels 54 and provides a mounting location for the othercomponents of the cart 50, including the table platform 58 and the driveassembly 60. The base 52 is typically about 8 inches to about 24 inches(e.g., about 8 inches to 11 inches) wide by 6 inches to about 20 inches(e.g., 7 inches to 10 inches) deep and can be formed (e.g., molded,machined, and/or cast) of any of various suitable materials (e.g.,plastics, metals, and/or composites). The base 52 is designed tosufficiently support the other components of the cart 50. For example,the base can be made to support typically about 25 lbs to about 100 lbs.

The wheels 54 are fastened to the bottom of the base 52 so that the cart50 can be moved smoothly along typical floor surfaces. The wheels 54 aretypically casters (e.g., rigid or swivel casters) that can be made ofany of various suitable materials (e.g., plastics, metals, and/orcomposites).

The vertically moveable platform 56 is a substantially flat planarmember, similar to the base 52, that provides a seating location for thePD cycler 100. The vertically moveable platform 56 is typically about 8inches to about 24 inches (e.g., about 8 inches to 11 inches) wide by 6inches to about 20 inches (e.g., 7 inches to 10 inches) deep and can beformed (e.g., molded, machined, and/or cast) of any of various suitablematerials (e.g., plastics, metals, and/or composites). The verticallymoveable platform 56 is designed to sufficiently support the weight ofthe PD cycler 100 while stationary, as well as when articulating up anddown. For example, the vertically moveable platform can be made tosupport typically about 35 lbs to about 60 lbs. During PD treatments,the vertically moveable platform 56 moves up and down via the driveassembly 60, as discussed below. The vertically moveable platform 56also includes an extension 62 that contains certain components of thedrive assembly 60, as discussed below.

The drive assembly 60 is used to move the vertically moveable platform56 and the PD cycler 100 seated on the vertically moveable platform 56up and down in a controlled and monitored manner during PD treatments.The drive assembly 60 is configured to move the vertically moveableplatform 56 over a height range that is typically greater than 24 inches(e.g., about 24 inches to about 48 inches). The drive assembly 60includes a leadscrew 64 and a leadscrew nut 66 that is rotated andcontrolled by a motor 68 during articulation. The leadscrew 64 ismounted to the base 52 in a fixed position and extends upward from thebase 52. The motor 68 and leadscrew nut 66 are contained in thevertically moveable platform 56. As shown, the leadscrew nut 66 ispositioned in the extension 62 of the vertically moveable platform 56 sothat it can engage the leadscrew 64. The leadscrew nut 66 is coupled tothe extension 62 such that the leadscrew nut 66 is able to rotate aboutits central axis with respect to the vertically moveable platform 56 andthe extension 62 (e.g., via bearings that connect the leadscrew nut 66to vertically moveable platform 56), but it is constrained from movingin a vertical direction with respect to the vertically moveable platform56 and the extension 62. Therefore, as the electric motor 68 rotates theleadscrew nut 66, the leadscrew nut 66 rotates about the stationaryleadscrew 64 and therefore travels upward or downward along threads ofthe leadscrew 64 depending on the direction of rotation of the leadscrewnut 66.

The drive assembly 60 includes an alignment mechanism that prevents thevertically moveable platform 56 from rotating around the leadscrew 64 asthe leadscrew nut 66 rotates. Although the leadscrew nut 66 is typicallyable to rotate freely within the extension 62 of the vertically moveableplatform 56, frictional and/or inertial forces caused by the rotatingleadscrew nut 66 could potentially cause the vertically moveableplatform 56 to also rotate about the leadscrew 64. To prevent rotationof the vertically moveable platform 56, the leadscrew 64 includes arecessed channel 70 within the leadscrew threads that extends uniformlyalong the longitudinal direction of the leadscrew 64. To engage therecessed channel 70, the vertically moveable platform 56 includes a tabfeature 72 that is sized to fit within the recessed channel 70. As theleadscrew nut 66 rotates around the stationary leadscrew 64 andarticulates upward or downward, the tab 72 moves vertically within therecessed channel 70 and prevents the vertically moveable platform 56from rotating. In some examples, the tab 72 includes linear bushings orbearings to provide smooth translation along the recess 70.

The motor 68 is an electric motor (e.g., an electric stepper motor,other types of DC motors, or an AC motor) that is mechanically connectedto the leadscrew nut 66 using gears to provide rotation to the leadscrewnut 66. The motor 68 includes electrical connections (e.g., wiringand/or a wire harness) to electrically connect the motor 68 to the PDcycler 100 to be used with the cart so that the PD cycler 100 cancontrol the motion as well as monitor the position of the verticallymoveable platform 56. During use, the PD cycler 100 can monitor theposition of the vertically moveable platform 56 by monitoring therotation of the motor 68. By knowing an initial position (e.g., a homeposition) of the vertically moveable platform 56, the PD cycler 100 cancount the number of stepper motor rotations or steps in order tocalculate the upward or downward travel and therefore the position ofthe vertically moveable platform 56. By monitoring the number of motorsteps, the distance of upward or downward travel of the verticallymoveable platform 56 can be determined using the pitch of the leadscrewthreads. To calibrate the cart 50 and the PD cycler 100, the initialposition (e.g., the height during assembly or installation) of thevertically moveable platform 56 and the distance that the verticallymoveable platform 56 travels during each motor step can be coded intothe software of the PD cycler 100. The initial position and the distancetravelled per step can then be used to determine current position at agiven time during operation of the cart 50 by counting the number ofmotor steps. In some implementations, other calibration techniques arepossible.

The table platform 58 is a substantially rigid planar member mounted tothe base 52 using leg members 74. Like the vertically moveable platform56, the table platform 58 can be formed (e.g., molded, machined, and/orcast) of any of various suitable materials (e.g., plastics, metals,and/or composites). The table platform 58 is mounted to the base 52using the leg members 74 so that the table platform 58 is at a heightthat corresponds with a typical height of a patient during typical PDtreatments. For example, the table platform can be positioned about 25inches to about 30 inches (e.g., about 27 inches) above the groundsurface. The leg members 74 are elongated beams that can be formed ofany of various suitable materials (e.g., beams, tubing, and/or othermembers). The leg members 74 have sufficient column strength to supportthe weight of the table platform 58 along with any equipment that istypically disposed on the table platform 58. For example, the legmembers can be designed to support typically about 30 lbs to about 50lbs. As shown in FIG. 2, the table platform 58 is generally u-shaped andincludes an opening 76 that is sized so that the vertically moveableplatform 56 and the extension 62 are not obstructed while they move upand down along the leadscrew 64. Because the table platform 58 isu-shaped, fluid lines that extend from the front of the PD cycler 100will typically not get hung up during use.

Referring back to FIG. 1, dialysis solution bags 122 are suspended fromfingers (e.g., hooks) 123 on the sides of the cart 50, and a heater bag124 is positioned on the heater tray 116. The dialysis solution bags 122and the heater bag 124 are connected to the cassette 112 via dialysissolution bag lines 126 and a heater bag line 128, respectively. Thedialysis solution bag lines 126 can be used to pass dialysis solutionfrom dialysis solution bags 122 to the cassette 112 during use, and theheater bag line 128 can be used to pass dialysis solution back and forthbetween the cassette 112 and the heater bag 124 during use. In addition,a patient line 130 and a drain line 132 are connected to the cassette112. The patient line 130 can be connected to a patient's abdomen via acatheter and can be used to pass dialysis solution back and forthbetween the cassette 112 and the patient during use. The drain line 132can be connected to a drain or drain receptacle and can be used to passdialysis solution from the cassette 112 to the drain or drain receptacleduring use.

Peritoneal Dialysis Machine

As shown in FIG. 3, the PD cycler 100 includes a housing 106, a door108, and a cassette interface 110 that abuts a disposable PD cassette112 when the cassette 112 is disposed within a cassette compartment 114formed between the cassette interface 110 and the closed door 108. Aheater tray 116 is positioned on top of the housing 106. The heater tray116 is sized and shaped to accommodate a bag of dialysis solution (e.g.,a 5 liter bag of dialysis solution). The PD cycler 100 also includes adisplay (e.g., a touch screen or conventional screen) 118 and additionalcontrol buttons 120 that can be operated by a user (e.g., a patient) toallow, for example, set-up, initiation, and/or termination of a PDtreatment.

FIG. 4 shows a more detailed view of the cassette interface 110 and thedoor 108 of the PD cycler 100. As shown, the PD cycler 100 includespistons 133A, 133B with piston heads 134A, 134B attached to pistonshafts that can be axially moved within piston access ports 136A, 136Bformed in the cassette interface 110. The piston shafts are connected tomotors that can be operated to move the piston heads 134A, 134B axiallyinward and outward within the piston access ports 136A, 136B. Asdiscussed below, when the cassette 112 (shown in FIGS. 3 and 5-7) ispositioned within the cassette compartment 114 of the PD cycler 100 withthe door 108 closed, the piston heads 134A, 134B of the PD cycler 100align with pump chambers 138A, 138B of the cassette 112 such that thepiston heads 134A, 134B can be mechanically connected to fasteningmembers of the cassette 112 overlying the pump chambers 138A, 138B. As aresult of this arrangement, movement of the piston heads 134A, 134Btoward the cassette 112 during treatment can decrease the volume of thepump chambers 138A, 138B, and force dialysis solution out of the pumpchambers 138A, 138B, while retraction of the piston heads 134A, 134Baway from the cassette 112 can increase the volume of the pump chambers138A, 138B and cause dialysis solution to be drawn into the pumpchambers 138A, 138B.

Still referring to FIG. 4, the PD cycler 100 also includes multipleinflatable members 142 positioned within inflatable member ports 144 inthe cassette interface 110. The inflatable members 142 align withdepressible dome regions 146 of the cassette 112 (shown in FIGS. 5-7)when the cassette 112 is positioned within the cassette compartment 114of the PD cycler 100. While only one of the inflatable members 142 islabeled in FIG. 4, it should be understood that the PD cycler 100includes an inflatable member associated with each of the depressibledome regions 146 of the cassette 112. The inflatable members 142 act asvalves to direct dialysis solution through the cassette 112 in a desiredmanner during use. In particular, the inflatable members 142 bulgeoutward beyond the surface of the cassette interface 110 and intocontact with the depressible dome regions 146 of the cassette 112 wheninflated, and retract into the inflatable member ports 144 and out ofcontact with the cassette 112 when deflated. By inflating certaininflatable members 142 to depress their associated dome regions 146 onthe cassette 112, certain fluid flow paths within the cassette 112 canbe occluded. Thus, PD solution can be pumped through the cassette 112 byactuating the piston heads 134A, 134B, and can be guided along desiredflow paths within the cassette 112 by selectively inflating anddeflating the inflatable members 142.

The door 108 of the PD cycler 100, as shown in FIG. 4, definescylindrical recesses 152A, 152B that substantially align with thepistons 133A, 133B when the door 108 is in the closed position. When thecassette 112 (shown in FIGS. 5-7) is positioned within the cassettecompartment 114, hollow projections 154A, 154B of the cassette 112,inner surfaces of which partially define the pump chambers 138A, 138B,fit within the recesses 152A, 152B. The door 108 further includes a padthat is inflated during use to compress the cassette 112 between thedoor 108 and the cassette interface 110. With the pad inflated, theportions of the door 108 forming the recesses 152A, 152B support theprojections 154A, 154B of the cassette 112 and the planar surface of thedoor 108 supports the other regions of the cassette 112. The door 108can counteract the forces applied by the inflatable members 142 and thusallows the inflatable members 142 to actuate the depressible domeregions 146 on the cassette 112. The engagement between the door 108 andthe hollow projections 154A, 154B of the cassette 112 can also help tohold the cassette 112 in a desired fixed position within the cassettecompartment 114 to further ensure that the pistons 133A, 133B align withthe fluid pump chambers 138A, 138B of the cassette 112.

FIG. 5 is a perspective, cross-sectional view of the cassette 112, andFIGS. 6 and 7 are perspective views of the cassette 112, from themembrane side and from the rigid base side, respectively. Referring toFIGS. 5 and 6, the cassette 112 includes a flexible membrane 140attached to a periphery of a tray-like rigid cassette base 156. Rigiddome-shaped fastening members 161A, 161B are positioned within recessedregions 162A, 162B of the cassette base 156. The dome-shaped members161A, 161B are sized and shaped to receive the piston heads 134A, 134Bof the PD cycler 100. The annular flanges 164A, 164B of the rigiddome-shaped members 161A, 161B are attached in a liquid-tight manner toportions of the inner surface of the membrane 140 surroundingsubstantially circular apertures 166A, 166B formed in the membrane 140.The apertures 166A, 166B expose the rigid dome-shaped members 161A, 161Bsuch that the piston heads 134A, 134B are able to directly contact andmechanically connect to the dome-shaped members 161A, 161B during use.

The annular flanges 164A, 164B of the dome-shaped members 161A, 161B, asshown in FIG. 5, form annular projections 168A, 168B that extendradially inward and annular projections 176A, 176B that extend radiallyoutward from the side walls of the dome-shaped members 161A, 161B. Whenthe piston heads 134A, 134B are mechanically connected to thedome-shaped members 161A, 161B, the radially inward projections 168A,168B engage the rear angled surfaces of the sliding latches 145A, 145Bof the piston heads 134A, 134B to firmly secure the dome-shaped members161A, 161B to the piston heads 134A, 134B. Because the membrane 140 isattached to the dome-shaped members 161A, 161B, movement of thedome-shaped members 161A, 161B into and out of the recessed regions162A, 162B of the cassette base 156 (e.g., due to reciprocating motionof the pistons 133A, 133B) causes the flexible membrane 140 to similarlybe moved into and out of the recessed regions 162A, 162B of the cassettebase 156. This movement allows fluid to be forced out of and drawn intothe fluid pump chambers 138A, 138B, which are formed between therecessed regions 162A, 162B of the cassette base 156 and the portions ofthe dome-shaped members 161A, 161B and membrane 140 that overlie thoserecessed regions 162A, 162B.

Referring to FIG. 6, raised ridges 167 extend from the substantiallyplanar surface of the cassette base 156 towards and into contact withthe inner surface of the flexible membrane 140 when the cassette 112 iscompressed between the door 108 and the cassette interface 110 of the PDcycler 100 to form a series of fluid passageways 158 and to form themultiple, depressible dome regions 146, which are widened portions(e.g., substantially circular widened portions) of the fluid pathways158, as shown in FIG. 6. The fluid passageways 158 fluidly connect thefluid line connectors 160 of the cassette 112, which act as inlet/outletports of the cassette 112, to the fluid pump chambers 138A, 138B. Asnoted above, the various inflatable valve members 142 of the PD cycler100 act on the cassette 112 during use. During use, the dialysissolution flows to and from the pump chambers 138A, 138B through thefluid pathways 158 and dome regions 146. At each depressible dome region146, the membrane 140 can be deflected to contact the planar surface ofthe cassette base 156 from which the raised ridges 167 extend. Suchcontact can substantially impede (e.g., prevent) the flow of dialysissolution along the region of the pathway 158 associated with that domeregion 146. Thus, the flow of dialysis solution through the cassette 112can be controlled through the selective depression of the depressibledome regions 146 by selectively inflating the inflatable members 142 ofthe PD cycler 100.

Still referring to FIG. 6, fluid line connectors 160 are positionedalong the bottom edge of the cassette 112. As noted above, the fluidpathways 158 in the cassette 112 lead from the pumping chambers 138A,138B to the various connectors 160. The connectors 160 are configured toreceive fittings on the ends of the dialysis solution bag lines 126, theheater bag line 128, the patient line 130, and the drain line 132. Oneend of the fitting can be inserted into and bonded to its respectiveline and the other end can be inserted into and bonded to its associatedconnector 160. By permitting the dialysis solution bag lines 126, theheater bag line 128, the patient line 130, and the drain line 132 to beconnected to the cassette, as shown in FIGS. 1 and 3, the connectors 160allow dialysis solution to flow into and out of the cassette 112 duringuse.

As noted above, the membrane 140 is attached to the periphery of thecassette base 156 and to the annular flanges 164A, 164B of thedome-shaped members 161A, 161B. The portions of the membrane 140overlying the remaining portions of the cassette base 156 are typicallynot attached to the cassette base 156. Rather, these portions of themembrane 140 sit loosely atop the raised ridges 165A, 165B, and 167extending from the planar surface of the cassette base 156.

The technique and pumping operation used to draw dialysis solution intothe pump chamber 138A and to force dialysis solution out of the pumpchamber 138A and that of pump chamber 138B are identical and thus suchtechniques and operations are discussed with regards to pump chamber138A and are not separately described in detail with regards to pumpchamber 138B.

As shown in FIG. 8, during installation, the door 108 of the PD cycler100 is opened to expose the cassette interface 110 and the cassette 112is positioned adjacent to the cassette interface 110 with dome-shapedmembers 161A, 161B aligned with the pistons 133A, 133B of the PD cycler100 and with its membrane 140 adjacent to the cassette interface 110.The pistons 133A, 133B are typically retracted into the piston accessports 136A, 136B during installation of the cassette 112 to avoidinterference between pistons 133A, 133B and the dome-shaped members161A, 161B and thus increase the ease with which the cassette 112 can bepositioned within the cassette compartment 114. Once the cassette 112 isproperly in position, the door 108 can be closed over the cassette 112such that the cassette 112 is contained within the cassette compartment114 between the door 108 and the cassette interface 110. With thecassette 112 positioned in the cassette compartment 114 and the door 108closed, the inflatable pad within the door 108 is inflated to compressthe cassette 112 between the door 108 and the cassette interface 110.This compression of the cassette 112 holds the projection 154A of thecassette 112 in the recess 152A of the door 108 and presses the membrane140 tightly against the raised ridges 167 extending from the planarsurface of the rigid base 156 to form the enclosed fluid pathways 158and dome regions 146.

Once the cassette 112 has been installed within the cassette compartment114 of the PD cycler 100, the piston 133A is advanced to initiate theprocess of mechanically connecting the piston head 134A of the PD cycler100 to the dome-shaped member 161A of the cassette 112. The piston 133Aincludes a latch-type device that engages the dome shaped member 161A.To engage the latch-type device, the piston 133A continues to advancetoward the cassette 112 until latches contact and engage the dome shapedmember 161A for operation of the PD cycler.

After the piston 133A has been mechanically connected to the dome-shapedmember 161A, the piston 133A is retracted to draw dialysis solution intothe pump chamber 138A. Because the piston head 134A is mechanicallyconnected to the dome-shaped member 161A and the dome-shaped member 161Ais attached to the membrane 140 of the cassette 112, the retraction ofthe piston 133A causes the dome-shaped member 161A and the portion ofthe membrane 140 attached to the dome-shaped member 161A to moverearwardly. As a result, the volume of the pump chamber 138A isincreased and fluid is drawn into the pump chamber 138A.

Because the volumes of the fluid pump chamber 138A and the piston head134A are known, the linear distance travelled by the piston 133A can beused to determine the volume of dialysis solution drawn into the fluidpump chamber 138A. The linear distance travelled by the piston 133A canbe determined based on the number of revolutions or steps of the motor(e.g., stepper motor) used to drive the piston 133A. Thus, the volume ofsolution drawn into the fluid pump chamber 138A can be determined basedon the number of revolutions or steps of the motor. The tight fitbetween the piston head 134A and the dome-shaped member 161A ensure theaccuracy of the volume of solution determined in this manner.

After drawing the dialysis solution into the pump chamber 138A, thedialysis solution is forced out of the pump chamber 138A by againadvancing the piston 133A and decreasing the volume of the pump chamber138A. The piston 133A is typically advanced until the dome-shaped member161A contacts or nearly contacts the inner surface of the recessedregion of the cassette base 156 so that substantially all of thedialysis solution is forced out of the fluid pump chamber 138A via theoutlet port 187A.

This process of drawing dialysis solution into the fluid pump chamber138A and then forcing the dialysis solution out of the fluid pumpchamber 138A is repeated until a desired volume of dialysis solution hasbeen pumped to or from a location (e.g., to or from the patient).

As noted above, while forcing dialysis solution into and out of the pumpchambers 138A, 138B, certain inflatable members 142 of the PD cycler 100can be selectively inflated to direct the pumped dialysis solution alongdesired pathways in the cassette 112.

Referring back to FIGS. 1 and 3, during PD treatment, the patient line130 is connected to a patient's abdomen via a catheter, and the drainline 132 is connected to a drain or drain receptacle. The PD treatmenttypically begins by emptying the patient of spent dialysis solution thatremains in the patient's abdomen from the previous treatment. To dothis, the pump of the PD cycler 100 is activated to cause the pistons133A, 133B to reciprocate and selected inflatable members 142 areinflated to cause the spent dialysis solution to be drawn into the fluidpump chambers 138A, 138B of the cassette 112 from the patient. The spentdialysis solution is then pumped from the fluid pump chambers 138A, 138Bto the drain via the drain line 132.

After draining the spent dialysis solution from the patient, heateddialysis solution is transferred from the heater bag 124 to the patient.To do this, the motor or motors of the PD cycler 100 is/are activated tocause the pistons 133A, 133B to reciprocate and certain inflatablemembers 142 of the PD cycler 100 are inflated to cause the warmeddialysis solution to be drawn into the fluid pump chambers 138A, 138B ofthe cassette 112 from the heater bag 124 via the heater bag line 128.The warmed dialysis solution is then pumped from the fluid pump chambers138A, 138B to the patient via the patient line 130.

Once the dialysis solution has been pumped from the heater bag 124 tothe patient, the dialysis solution is allowed to dwell within thepatient for a period of time. During this dwell period, toxins cross theperitoneum of the patient into the dialysis solution from the patient'sblood. As the dialysis solution dwells within the patient, the PD cycler100 prepares fresh dialysate for delivery to the patient in a subsequentcycle. In particular, the PD cycler 100 pumps fresh dialysis solutionfrom one of the four full dialysis solution bags 122 into the heater bag124 for heating. To do this, the pump of the PD cycler 100 is activatedto cause the pistons 133A, 133B to reciprocate and certain inflatablemembers 142 of the PD cycler 100 are inflated to cause the dialysissolution to be drawn into the fluid pump chambers 138A, 138B of thecassette 112 from the selected dialysis solution bag 122 via itsassociated line 126. The dialysis solution is then pumped from the fluidpump chambers 138A, 138B to the heater bag 124 via the heater bag line128.

After the dialysis solution has dwelled within the patient for thedesired period of time, the spent dialysis solution is pumped from thepatient to the drain. The heated dialysis solution is then pumped fromthe heater bag 124 to the patient where it dwells for a desired periodof time. These steps are repeated with the dialysis solution from two ofthe three remaining dialysis solution bags 122. The dialysis solutionfrom the last dialysis solution bag 122 is typically delivered to thepatient and left in the patient until the subsequent PD treatment.

After completion of the PD treatment, the pistons 133A, 133B areretracted in a manner to disconnect the piston heads 134A, 134B from thedome-shaped members 161A, 161B of the cassette.

After the pistons 133A, 133B have been disconnected from and backed outof the dome-shaped members 161A, 161B of the cassette 112 in the mannerdescribed above, the door 108 of the PD cycler is opened and thecassette 112 is removed from the cassette compartment 114 and discarded.

Monitoring Fluid Pressure

It is advantageous to be able to accurately monitor and control pressurebetween the pump chambers 138A, 138B of the cassette 112 and thepatient. If the pressure within a line to the patient increases abovemaximum limits, harm can be caused to the patient.

To monitor the pressure in the system, two pressure sensors 131 (shownin FIG. 4) are utilized to indirectly detect the pressure and vacuumwithin the patient's peritoneum. These sensors are preferably solidstate silicon diaphragm infusion pump force/pressure transducers, forexample Model 1865 made by Sensym Foxboro ICT. When the cassette 112(shown in FIGS. 3 and 5-8) is inserted into the cassette compartment114, the pressure sensing areas “P” within the cassette 112 (shown inFIG. 6) line up and are in intimate contact with the two pressuresensors 131. These sensing areas P are connected, respectively, directlyto each pump chamber 138A, 138B through canals 137A and 137B,respectively, so that when fluid moves in and out of the chambers 138A,138B, the pressure sensors 131 can detect its presence. The cassettemembrane includes two areas marked “P” adheres to the pressure sensors131 using vacuum pressure. Clearance around the pressure sensorscommunicates vacuum to the pressure dome diaphragms the circumferencesof which are sealed airtight to the cassette deck by the pressurizationof the door compartment.

The two pressure sensors 131 are connected to a high resolution 24 bitSigma-Delta, serial output A-D converter (ADC) on an I/O board. This ADCsends a signal from each of the two pressure sensors to the FPGA on theboard. After the data ready signal is received by the FPGA, the FPGAreads this ADC and transfers this data to be processed by themicroprocessor, which in the preferred implementation of the inventionis an MPC823 PowerPC device manufactured by Motorola, Inc.

On completion of the flush and prime processes, the cassette will befilled with solution. At this time, the line to the patient will becompletely filled with solution. The pressure at this stage is detectedand will be used as base line for static pressure. At that time, thepatient's head height relative to the PD cycler will be determined fromthe differential in the pressure reading. Preferably, this pressuredifferential is maintained below 100 mbar.

During the drain sequence, it is advantageous to hold the vacuum in theperitoneum at or above −100 mbar.

Since continuous flow through the various lines connected to the patientis essential to proper treatment of the patient, it is important tocontinuously monitor if a patient line is blocked, partially blocked oropen. There are three different possible situations:

1. the patient line is open;

2. the patient line is closed; or

3. the patient line is not completely open and therefore creates anundesired flow resistance (caused, for example by the patient is lyingon the line).

The pressure sensors 131 (shown in FIG. 4) can be used to detect errorconditions. For example, when the piston 133A is protracting and therebypumping dialysate fluid into a line that is open to patient, it isadvantageous that the patient pressure and the encoder values can becarefully monitored, using the pressure sensors 131 described above.Three possible error situations may occur, for example, as a result ofthe following events:

1. The patient line is open when piston 133A is protracting until adefined length value is reached, and the patient pressure is notincreasing;

2. The patient line is closed, and the piston 133A is not able toprotract because the patient pressure increases to a defined alarmlimit.

3. The piston 133A protracts to produce an increasing patient pressure,but the pressure decreases slowly.

These error conditions may be sensed using the pressure sensors 131, andcorrective action can then be taken. Although corrective action could bein the form of sending an alarm to the patient, where the screen tellsthe patient what action to take, utilizing the methods described hereincan address some errors automatically without disturbing the patient.

Cart Uses

During PD treatments fluid resistance can build within the line that isconnected to a patient's abdomen via a catheter and used to passdialysis solution back and forth between the cassette and the patient.Such resistance can be caused by several factors, such as kinks in thepatient line caused by the patient lying on the line or other externalline obstructions, excess levels of fibrin present in the patient line,catheter obstructions within the patient's abdomen, and/or other issues.As discussed above, the resistance within the patient line can bedetected using the pressure sensors that measure the pressure in pumpchambers 138A, 138B. Typically, when the pressure builds in the patientline to a level that may be dangerous to the patient (e.g., 150-200mbar), an alarm will sound indicating that an error exists and needs tobe addressed. In some cases, an audible alarm will sound that willawaken the patient undergoing PD treatment so that the patient canaddress the problem (e.g., by adjusting the line or taking alternateaction). This awakening of the patient can result in an uncomfortable,disturbing, and/or undesirable PD treatment. Alternatively to soundingan alarm, the PD cycler pumps can be turned off to allow the pressure toreduce to acceptable levels. However, turning off the PD cycler pumpsalso results in delayed or incomplete and therefore sometimes equallyundesirable PD treatment. Therefore, any reduction in the frequency ofsuch alarms or interruptions to the PD treatment by automaticallyaddressing the errors can provide a more comfortable and, in some cases,a safer PD treatment for the patient.

The cart 50 described herein can be used to automatically address someerrors that occur during PD treatments caused by resistance in thepatient line. In order to automatically address errors, as shown in FIG.1, the PD cycler 100 is seated on the vertically moveable platform 56that is positioned at a home position (e.g., along the plane of thetable platform 58) at substantially the same height as the patient. Asdiscussed below, the PD cycler 100 can be raised and/or lowered usingthe drive assembly 60 to accommodate for pressure build-up duringfilling and/or draining of PD solution during treatments.

When high resistance levels are detected by the pressure sensors 131during filling, the PD cycler 100 can automatically reduce the pumpspeeds to prevent the pressure from continuing to increase to levelsthat could be potentially dangerous. However, in doing so, reducing thepump speeds can also cause the PD solution flow rates to decrease, andin some cases the flow to the patient can cease. Therefore, to maintainflow of PD solution to the patient while the pump speed is lowered, thevertically moveable platform 56 is raised to a height that is above thepatient so that the static pressure difference within the patient linewill cause the flow rate to increase or to be maintained at desiredlevels.

Similarly, when high resistance levels are detected by the pressuresensors 131 during draining, the PD cycler 100 can automatically reducethe pump speeds to prevent the pressure from continuing to increase tolevels that could potentially be dangerous. Like during filling,reducing the pump speeds can cause the flow rate of PD solution from thepatient to begin to decrease. However, instead of raising the PD cycler100 using the drive assembly 60 as done during filling, the cart 50lowers the PD cycler 100 to a height that is below the patient. Bylowering the PD cycler 100, the static pressure difference within thepatient line will cause the flow rate of PD solution from the patient toincrease or to be maintained at desired levels.

Example of Use of PD Cycler on a Cart During Draining

In one example of a PD treatment, during a normal draining process, PDsolution flows from a patient at an average flow rate of 200 ml/minuteand at an average pressure of 60-70 mbar, during which the pump of thePD cycler 100 is operated at a pump speed of 80. The pump speed isassociated with the rate of at which a leadscrew within the pump isrotated to move the pistons 133A, 133B in and out of the pump chamber,which can range from 5-140 during operation, for example, when using aLiberty PD cycler from Fresenius Medical Care NA.

During PD treatments, as discussed herein, certain events can occur(e.g., a line can become kinked or a catheter can become positionedagainst an obstruction in the patient) that cause resistance thatopposes the fluid from draining from a patient and causes pressure tobuild within the patient line. As fluid resistance continues to buildwithin the patient line, the pressure that is measured within the pumpchamber will also continue to increase. Instead of waking up the patientor sounding an alarm to address the issue before the pressure levelreaches a dangerous level (e.g., 150-200 mbar), as would typically bedone when using certain conventional PD systems, the PD cycler pumps areslowed gradually (e.g., by increments of 10) to reduce the high dynamicpressure caused by the fluid flow in the patient line. The pump speedcan be reduced to by 10 while the pressure within the line iscontinuously monitored. If the pressure does not drop to withinacceptable limits (e.g., less than 150 mbar), the pump speed is againreduced by 10 and the pressure within the line is monitored. Whilemonitoring the pressure, the pump speed is reduced incrementally untilthe pressure drops to within acceptable limits (e.g., less than 150mbar). However, when the PD cycler 100 is held at a constant verticalheight, reducing the pump speed typically causes the flow rate todecrease. For example, a pump speed reduction of 5-10 can result in aflow rate drop of about 20 ml/min and a pump speed reduction of 40 to 50can result in a flow rate drop of about 100 ml/min. Since reducing thepumps speed typically reduces the flow rate, the PD cycler 100 seated onthe vertically moveable platform 56 is lowered below the patient (e.g.,5 inches-20 inches) gradually to increase or maintain the flow rate(e.g., within 150 ml/min to 200 ml/min) of fluid draining from thepatient. Lowering the PD cycler 100 allows for draining fluid from thepatient at a higher fluid flow rate, while avoiding dangerously highpressures and/or disruption to the patient. Since the PD cycler 100 isable to control and monitor the position of the vertically moveableplatform 56 and the operation of the pump, the PD cycler 100 controlsthe position of vertically moveable platform 56 and the pump speed toimprove (e.g., optimize) the PD treatment by increasing (e.g.,maximizing) the flow rate while keeping the pressure below excessivelevels.

During the PD treatment, if the obstruction is removed and theresistance in the patient line is therefore reduced, the PD cycler 100can either allow the vertically moveable platform 56 to remain at thelowered height or raise the vertically moveable platform 56 to bring thePD cycler 100 back to a home position that is approximately level withthe patient. Instead of turning down the pumps and then adjusting theheight of the PD cycler 100 to compensate for the loss of fluid flow,alternatively, the PD cycler 100 can begin moving the verticallymoveable platform 56 and the PD cycler 100 downward while simultaneouslyslowing the pumps so that the loss of flow is minimized, in some casesthere is no loss of fluid flow.

While certain implementations have been described, other implementationsare possible.

While the drive assembly has been described as including a stationaryleadscrew and a rotating leadscrew nut, other configurations can beused. For example, in some implementations, the cart includes aleadscrew that can rotate and a leadscrew nut that is fixed to thevertically moveable platform.

While the drive assembly has been described as including a leadscrewassembly to move the vertically moveable platform, other devices can beused. In some implementations, the drive assembly includes a rack andpinion gear system, where the rack is positioned vertically and thepinion gear is mounted in the vertically moveable platform.

While the alignment mechanism has been described as including a recessin the leadscrew and a tab extending from a portion of the verticallymoveable platform, other alignment techniques can be used. In somecases, the drive assembly does not require an alignment mechanism.

In some implementations, the vertically moveable platform includes aretention device (e.g., a strap, screws, bolts, etc.) to secure the PDcycler during articulation.

While the PD cycler has been described as monitoring the position of thevertically moveable platform by counting the number of rotations of themotor which drives the drive assembly, other techniques can be used. Forexample, in some implementations, the drive assembly or verticallymoveable platform includes position sensors to determine the verticalposition of the vertically moveable platform.

While the motor has been described as being electrically connected tothe PD cycler in order to control the motor, other techniques can beused. In some implementations, the motor is electrically connected to aseparate control unit that is used to operate the motor and control theposition of the vertically moveable platform.

While the motor has been described as being connected to the leadscrewnut using gears, other techniques can be used. In some implementations,the drive assembly is driven by the motor using pulleys, chains, orother suitable techniques. Alternatively, in some implementations, themotor is an integrated component of the drive assembly.

While the cart has been described as including a table platform, in someimplementations, the cart does not include a table platform.

While the cart has been described as including three wheels, the cartcan include more or fewer wheels. For example, carts can include 2, 4,5, 6, or more wheels.

While the wheels have been described as being casters, other types ofsuitable wheels can be used.

In some implementations, one or more of the wheels include a lockingmechanism to temporarily secure the cart in place.

Alternatively, in some implementations, the cart does not includewheels.

While the piston heads have been described as including mechanical latchmechanisms with sliding latches that can be move radially inward andoutward to allow those piston heads to be mechanically connected todome-shaped members of the cassette, other piston heads canalternatively be used. In some implementations, other piston headsutilizing other mechanical engagement mechanisms of simpler constructionthat include no such sliding latches can alternatively be used in somecases. Alternatively, piston heads utilizing other engagement techniques(e.g., vacuum systems, adhesives, magnetics, or any other suitabletechniques) can be used to couple the pistons to the dome-shaped membersof the cassette or to the membrane of the cassette.

While the cassettes discussed above have two pump chambers, thecassettes can alternatively have more or fewer than two pump chambers.

While each of the pump chambers of the cassettes described above hasbeen described as including a fluid inlet port and a fluid outlet port,in certain implementations, the pump chambers include a single port thatis used as both an inlet and an outlet. In such implementations, theinflatable valve members of the PD cycler that act on the valve portionsof the cassettes would be activated and deactivated in a slightlydifferent sequence to allow fluid to be drawn into the pump chamber froma desired location and then to be forced out of the pump chamber to adesired location.

While the carts described above has been described as being associatedwith PD systems, these types of carts can be used in any of variousother types of medical fluid pumping systems. Other examples of medicalfluid pumping systems in which the carts described herein can be usedinclude hemodialysis systems, blood perfusion systems, intravenousinfusion systems, and other medical fluid handling systems.

What is claimed is:
 1. A method comprising: monitoring pressure in afluid path between a dialysis fluid pump chamber and a patient; andadjusting a vertical position of a dialysis machine when monitoredpressure exceeds a maximum pressure or falls below a minimum pressure.2. The method of claim 1, further comprising adjusting a rate at whichfluid is pumped to or from the patient along the fluid path.
 3. Themethod of claim 1, wherein adjusting the vertical position of thedialysis machine when monitored pressure exceeds a maximum pressurecomprises moving the dialysis machine upward vertically while fluid isbeing provided to the patient.
 4. The method of claim 3, wherein themaximum pressure is 150-200 mbar.
 5. The method of claim 3, furthercomprising reducing a rate at which fluid is pumped to the patient. 6.The method of claim 1, wherein adjusting the vertical position of thedialysis machine when monitored pressure falls below a minimum pressurecomprises moving the dialysis machine downward vertically while fluid isbeing removed from the patient.
 7. The method of claim 6, wherein theminimum pressure is (−150)-(−200) mbar.
 8. The method of claim 6,further comprising reducing a rate at which fluid is pumped from thepatient.
 9. The method of claim 1, wherein adjusting the verticalposition of the dialysis machine comprises adjusting a vertical positionof a platform on which the dialysis machine is supported.
 10. The methodof claim 9, wherein adjusting the vertical position of the platform onwhich the dialysis machine is supported comprises operating a driveassembly configured to move the platform vertically.
 11. The method ofclaim 10, wherein the drive assembly comprises: a leadscrew fixed to abase; a leadscrew nut that is rotatably coupled to the platform andengages the leadscrew; and a motor that is mechanically connected to theleadscrew nut and rotates the leadscrew nut.
 12. The method of claim 11,wherein: the leadscrew has a recess formed longitudinally along theleadscrew; and the platform has a tab that fits within the recess andtravels along the recess when the platform moves vertically.
 13. Themethod of claim 1, wherein the pressure is monitored by a sensor that isdisposed along the fluid path between the dialysis fluid pump chamberand the patient.
 14. The method of claim 1, wherein the verticalposition of the dialysis machine is adjusted 24-48 inches.
 15. Themethod of claim 1, wherein a control unit adjusts the vertical positionof the dialysis machine.
 16. The method of claim 15, wherein the controlunit comprises a microprocessor of the dialysis machine.
 17. The methodof claim 1, wherein the dialysis machine is a peritoneal dialysiscycler.
 18. The method of claim 1, further comprising operating a fluidpump of the dialysis machine to deliver fluid through the fluid pathfrom the dialysis fluid pump chamber to the patient while monitoring thepressure in the fluid path.
 19. The method of claim 18, whereinadjusting the vertical position of the dialysis machine comprisesadjusting a vertical position of a platform on which the dialysismachine including the fluid pump is supported.
 20. The method of claim1, further comprising operating a fluid pump of the dialysis machine todraw fluid from a dialysate fluid container into the dialysis fluid pumpchamber and to deliver the fluid through the fluid path from thedialysis fluid pump chamber to the patient while monitoring the pressurein the fluid path.
 21. The method of claim 1, further comprisingoperating a fluid pump of the dialysis machine to draw fluid from adialysate fluid container into the dialysis fluid pump chamber and todeliver the fluid through the fluid path from the dialysis fluid pumpchamber to the patient while monitoring the pressure in the fluid path.22. A method comprising: detecting, in a fluid path between a patientand a dialysis fluid pump chamber of a dialysis machine, a pressure thatdiffers from a predetermined pressure using a pressure sensor of thedialysis machine; and in response to detecting the pressure in the fluidpath that differs from the predetermined pressure, operating a motor toadjust a height of the dialysis machine.
 23. The method of claim 22,wherein operating the motor comprises operating a motor to adjust aheight of a platform on which the dialysis machine sits to adjust theheight of the dialysis machine.
 24. The method of claim 22, wherein thedetected pressure exceeds the predetermined pressure.
 25. The method ofclaim 22, wherein operating the motor comprises operating the motor tomove the dialysis machine downward vertically while fluid is beingremoved from a patient.
 26. The method of claim 22, wherein operatingthe motor comprises operating the motor to drive a leadscrew.
 27. Themethod of claim 22, further comprising operating a fluid pump of thedialysis machine to deliver fluid through the fluid path from thedialysis fluid pump chamber to the patient while monitoring the pressurein the fluid path.
 28. The method of claim 27, wherein operating themotor comprises operating the motor to adjust the height of a platformon which the dialysis machine including the fluid pump is supported.